1. Field of the Invention
The present invention relates to a paper feeding apparatus for an electrophotographic apparatus such as a copying machine and printer, and more specifically relates to the paper feeding apparatus that separates and feeds sheets of paper by air flow.
2. Description of the Related Art
An example of the conventional paper feeding device used for an electrophotographic apparatus, which is referred to as an air suction type or air separation type paper feeding device, is shown in FIG. 1.
In FIG. 1, sheets of paper 2 stacked on the paper elevating table 1 are controlled to be located at a constant height at all times by the paper upper face detection sensor 3 and the control member 4 for controlling the paper elevating table 1 according to information sent from the paper upper face detection sensor 3. The vacuum and air charging chamber 5, the belt member 6 having suction holes and the drive unit 7 for driving the belt member 6 are arranged in an upper portion of the sheets of paper 2. On the front face of the sheets of paper in the conveyance direction, the air injection nozzles 8 are provided so that the sheets of paper in the upper layer portion of the stacked sheets of paper can be separated from each other when air is blown, and the sheets of paper are floated. The sheet of paper 2 which has floated by the air injection nozzles 8 is sucked and conveyed by the belt member 6. In this way, paper feeding is conducted. In the downstream of the flow of the sheets of paper in the conveyance direction, the sheet conveyance member, which is a so-called conveyance roller 9, is provided which receives the sheet of paper 2, which is sucked and conveyed by the belt member 6, and conveys it to an image forming section not shown in the drawing.
In the paper feeding device composed as described above, in order to positively and quickly separate and float the sheet of paper by a current of air and convey it to the image forming section, various proposals have been conventionally made.
For example, in the official gazette of Japanese Patent No. 2934442, the paper separating and supplying device illustrated in FIGS. 2 and 3 is disclosed. This device can provide the following advantages. As shown in FIGS. 2 and 3, in addition to the air injection nozzles 8 for separating and floating the sheets of paper 2 when a current of air is blown to them, the second nozzles 10 for injecting air to the side of sheets of paper with respect to the conveyance direction of the sheets of paper 2 are provided so that the floating effect of the sheets of paper 2 can be enhanced.
However, the above structure has the following disadvantages. When the sheets of paper are thick and difficult to be floated by a current of air, the above structure is advantageous. On the other hand, when the sheets of paper are thin, for example, in the case of tracing paper, the thickness of which is small, the sheets of tracing paper are extremely floated and a large number of sheets of tracing paper are supplied at one time. Therefore, according to the type of paper, it is necessary to prepare a mode, in, which a current of air is injected from the front, and a mode in which currents of air are injected from both the front and the side. When necessary, the current of air must be switched.
Concerning the device for supplying air to the air injection nozzles 8, 10 and supplying and discharging air from the vacuum and air charging chamber 5, a fan or blower is commonly used. In general, in the case of an electrophotographic apparatus such as a copying machine or printer, a plurality of paper feeding devices are arranged in many cases. Therefore, the number of fans or blowers is increased, which raises the manufacturing cost.
A system in which a plurality of fans, which are used in the conventional image forming apparatus, are reduced to one or a small number is disclosed in the official gazette of JP-A-2002-169450. However, in any case, it is necessary to provide a plurality of distributing devices for distributing a current of air, which has been supplied from one set of fan or blower, to a plurality of passages or nozzles.
Further, in the case of the paper feeding device shown in FIGS. 2 and 3 in which air is injected in two directions, one is a direction to the front of the sheets of paper 2 and the other is a direction to the side of the sheets of paper 2, in order to control the current of air in the two directions, it is necessary to provide air supplying units which are respectively independent from each other. Alternatively, it is necessary to provide a distributing device for switching the current of air. As a result, the manufacturing cost of the entire device is increased.